This invention relates to lift trucks and, more particularly, to a new system for providing a digital display of inclination of a lift truck mast from a vertical.
In the use of lift trucks, which typically have a mast having forks, a platen, or some other lifting device or devices for lifting a load, it is conventional to provide for operator control of inclination of the mast relative to vertical, thereby allowing the operator to adjust forward and backward tilt of the mast, for example. Front tilt may be required for picking up or depositing a load while rear tilt may be required for safe carrying of the load from one position to the other. It may be necessary also to control orientation of the load when picking up or depositing same.
In some specialized lift trucks, such as those used for glass handling wherein large sheets of glass must be transported from one place to another, it is very important to dispose the sheets of glass, as when they are being stacked, so that they are oriented very close to level. Otherwise,, a stack of sheets varying even a few degrees from vertical will become unstable causing the lower sheets to slip out from the stack resulting in an extremely dangerous condition resulting in broken glass and setting serious life threatening potential. Stacking may be required to be level within .+-.0.5.degree..
Although it has been proposed to provide an analog display of lift mast inclination, such as in the arrangements disclosed in Brudi U.S. Pat. No. 3,865,265 and Wilhelm U.S. Pat. No. 3,883,021, it is found that lift truck operators can more effectively provide accurate adjustment of the lift mast inclination, such as orienting it at precisely 0.degree. inclination, if provided with a digital display of the inclination in degrees and increments of degrees. Also, analog arrangements have been prone to certain errors such as resulting from aging of components, drift, out-of-tolerance conditions, offset errors and so forth.
A further problem which has plagued prior art inclinometers is proneness to swinging or oscillation of pendulums or other masses used to detect alignment. To reduce such oscillation, it has been proposed, as in the above-identied patents, to use liquid damping of pendulums, etc., but this requires a complex sealing arrangement to prevent fluid leakage and consequent greater cost of manufacture.
It is an object of this invention to provide an inclinometer for an apparatus, such as a vehicle, indicating orientation of structure of such apparatus with respect to vertical.
It is a further object of this invention to provide such an inclinometer which displays, preferably in digital form, the degrees and increments of degrees of the orientation of a lift truck mast with respect to a true vertical gravitional plumb line for use by the lift truck operator for adjusting the orientation of the mast with respect to vertical.
A still further object of this invention is to provide such a digital inclinometer which can provide precise, accurate and easily determinable alignment of a lift truck mast to control load orientation when picking up, depositing, or carrying same, and particularly, for precisely orienting the mast of a specialized lift truck used for glass handling.
Another object of the invention is the provision of such a digital inclinometer which is not prone to errors resulting from aging of components, drift, or out-of-tolerance conditions, offset errors, and so forth, providing at all times a precise digital display of mast inclination.
Another object of the invention is the provision of such a digital inclinometer utilizing a sensor which is not prone to oscillation and which is inherently self-damping.
A further object of the present invention is the provision of such a digital inclinometer which is constructed of an absolute minimum of mechanical and moving components, which utilizes relatively few simple, lost cost optical sensing elements for sensing inclination and which provides solid state electronic conversion of the sensed inclination for use in displaying the inclination digitally.
Other objects of the invention include the provision of such a digital inclinometer which is rugged and reliable in usage; which is relatively immune from damage due to vibration, shock, or acceleration; which provides reliable display of inclination; and which gives to the operator automatic indication of any condition of excessive inclination which could not be electronically sensed and displayed.
Other objects and features will be in part apparent and in part pointed out hereinbelow.